Squash Vine Borers Collapse Plants

Gardeners are made of tough stuff. We manage a brave smile when our seedlings get nibbled, our leaves go spotty and the blessed groundhogs help themselves to our harvest.  

But there is one affliction that bring tears to our eyes: squash vine borers. I just felt the shudders from those of you who’ve had a close encounter. It’s awful.  

wilted squash plant
Squash vine borers cause the collapse of squash plants.

Picture if you will a robust squash plant, deep green, full of flowers and fruit, tall enough to shade several small children. The next morning as you sip your coffee, you spy it out your kitchen window, wilted, flattened, gone.

Yes, your neighbors heard you wail.  

What happened? Squash vine borers. These insidious insects tunnel inside squash as larvae, happily munching away as they fatten. Finally they hollow out enough of the plant that it collapses, its vascular system vanquished.

Squash vine borers most often hit summer and winter squash and pumpkins. But they can go after cucumbers, gourds and melons, too.  

So how do you prevent this tragedy? There are several good preventive measures and treatments.  

One trick is to plant early. Every insect has a prime time and simply planting earlier helps you avoid squash vine borers’ window of activity. It pays to know the enemy. 

Use established transplants instead of seeds or plant squash seeds mid-June. Again, it’s all about timing.  

You can prevent flying adults from laying eggs on your plants in May and June one of three ways. Wrap a collar of aluminum foil around the lower stems. Dust or spray with spinosad or pyrethrum. Or, cover your plants with floating row covers until they flower.  

Check your squash plants daily for signs of larval feeding. If a runner suddenly wilts, there’s probably a borer in there doing its worst.  

Also look at the base of your plants for holes and tan, sawdust-like bits. As borer larva feed, they push out frass, a fancy word for insect poop. If you find any, the game’s afoot.

squash vine damage from borer larvae
Squash vine borer larvae tunnel out the inside of squash plants.

Use a knife to make a slit upward from where you see frass. Cut halfway through the stem and remove and kill the larva, a white caterpillar with a dark head. Mound soil over the cut to promote healing. 

If you’re squeamish about squishing, inject Bt – a naturally occurring soil bacteria and organic insecticide – into the wound to kill the borer.  

If you remove an infested vine, seal it in a plastic bag and put it in the trash. This prevents the larva from dropping to the ground to pupate and return to infest your plants next year. 

I just heard Arnold say, “I’ll be back.”  

It also helps to know which squash the vine borers prefer. Butternut and cushaw squash are resistant to borers. Yellow crookneck squash is less likely to get borers than zucchini.  

Don’t give up on squash. I for one will not be without butternut squash soup. And Halloween without pumpkins is unthinkable. So prepare, prevent, and treat wisely to keep enjoying squash.

By Annette Cormany, Principal Agent Associate and Master Gardener Coordinator, Washington County, University of Maryland Extension. This article was previously published by Herald-Mail Media. Read more by Annette.

10 thoughts on “Squash Vine Borers Collapse Plants

  1. lilyo3 July 24, 2020 / 9:52 am

    I have found that tromboncino squash is also less susceptible to squash vine borers and squash bugs. They are a vining type of squash though and will need space to grow or climb.

    • Annette Cormany August 5, 2020 / 3:49 pm

      Thanks for sharing this!

  2. ejcT July 24, 2020 / 1:05 pm

    Excellent article. Thank you for your optimistic spirit and useful information A.Cormany.

    • Annette Cormany August 5, 2020 / 3:50 pm

      I’m glad you enjoyed it and found it helpful.

  3. Bob of Clarksville July 26, 2020 / 5:41 pm

    HGIC at one time recommended planting a squash crop late in the spring, say seeding second or third week of June, which is after most of the offending insects have finished their major breeding season. I’ve done that for years, and it seems to work well. Is that still a recommended “solution” to the squash vine borers?

  4. Phyll in Silver Spring July 28, 2020 / 11:55 pm

    I sowed my zucchini seeds in late May in Silver Spring which is my usual time. I never thought of this as early. I used row cover for a while and wrapped the lower stems with foil. The borers just entered the plants higher up. I read that a late planting may fall outside the borer’s active window so have some new starts almost ready to transplant. Fingers crossed.

  5. Patricia Shema September 22, 2020 / 12:45 pm

    I also have the dreaded squash borer, but that is not my real problem. Normally I have more squash than I can stand and the neighbors run away when they see me coming. The last 3 years I have had a reduced number of squash because there are few female flowers. Pollinators I have, and I hand pollinate as well.
    This year I planted a second crop and there are NO female flowers. I have tried several varieties. Other Master Gardeners seek my advice about this same issue and I do not haver an answer. CAN YOU HELP?

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